A known method of joining the ends of an industrial fabric is to use a polymeric monofilament pintle wire so as to provide an endless belt. Each end of the fabric is provided with outwardly extending loops whereby the two sets of loops can be intermeshed and when aligned provide a “tunnel” for the insertion of a pintle wire. A description of such a method can be found in U.S. Pat. No. 5,079,807 entitled “Shaped Pintle Wire for Paper Machine Clothing” which issued on Jan. 14, 1992 to Paul F. Hood.
In paper production, endless belts of fabric are key components to the forming, pressing, and drying steps performed by the machines used to manufacture the paper products. One of the functions of the belts can be viewed as comparable to that served by conveyor belts because aside from serving the other key purposes of support and de-watering they carry the wet fibrous sheet along as it is being converted into a paper product.
The known monofilament pintle wires heretofore used in paper production are round in cross-section and have a low tensile strength. The wires may have flaws in the monofilament structure and, as a result, the wires often break on insertion through the tunnel defined by the loops. Even more critically, the wires may break when the belt is in operation. This can lead to belt damage and necessitates the disposal of the belt before the end of its expected working life. These belts are extremely expensive and the loss of product and production time adds even more to the expense of a separated belt. Another problem with the known monofilament wires is that the diameters of the round cross-section wires are such that they do not fill the loop area or void and as such result in a high degree of localized permeability. This, once again, is of particular importance in the field of paper making where variations and permeability in the seam result in marking of the paper product on the belt. Accordingly, it is a general object of the present invention to provide an improved pintle having properties for dealing with the foregoing mentioned problems.
As an alternate, monofilament pintle wires which comprise polyamide have been resin-treated. The resin treatment involves impregnation with phenolic or epoxy polymer resins which are then cured. Other monofilament pintle wires have been used which comprise polyamide multi-filaments wrapped around a polyamide monofilament core. These known treatments and structures serve to give the polyamide multi-filament a stiffness akin to a monofilament. Resin treatment processes are a burden in terms of increased material cost and production times, as well as being increasingly environmentally unsound due to the fact that treatment with these resins requires a considerable amount of organic solvent. Furthermore, polyamides are generally lacking in abrasion resistance. Various pintle designs have been proposed to overcome some of the problems. For example, in the aforementioned patent to Hood various pintle shapes are described. In U.S. Pat. No. 5,049,425 entitled “Porous Yarn for OMS Pintles” which issued to Klaus M. Essele on Sep. 17, 1991 a pintle of braided yarn encompasses a core of monofilaments. In U.S. Pat. No. 5,503,195 entitled “Combination-Type Seaming Pintles With Wire Leader” which issued to Roy C. Edens, Jr. on Apr. 2, 1996 another pintle design is described for a papermaking fabric.
Another solution to some of the above-mentioned problems has been proposed in U.S. Pat. No. 6,060,161 which issued on Mar. 9, 2000 to William Daniel Aldrich. In the Aldrich patent a multi-filament pintle wire comprising a polyolefin material is described and a particularly preferred polyolefin is ultra high molecular weight polyethylene which is gel-spun. The gel-spun polyethylene is produced with a high degree of linear orientation and a high degree of crystallinity to give it its strength. This polyethylene is also abrasion resistant and moisture resistant.